Question

I’m trying to run an external program in Java and to read the output. The program is a Linux application in C++ that runs a data mining algorithm and prints the patterns found on standard output. I want to be able to read that output from my Java app and to show the patterns using a table. The problem is that the size of the output is quite big (as a test it produces 6.5MB in about 30 seconds). I’m using ProcessBuilder and reading the output using an InputStreamReader buffered using a BufferedReader as you can see in the following code:

      String[] cmd = {"./clogen_periodic", selected, support, "-t 4"};
      Process p = new ProcessBuilder(cmd).start();
      input = new BufferedReader (new InputStreamReader(p.getInputStream()));

      while ((line = input.readLine()) != null) {
         ...
         process line;
         ...
      }

The problem is that the output gets corrupted. When I execute the same program on a console the output is correct but when I use the Java app some lines are merged. More precisely output should be like this

      TMEmulation log_pseduo_allocation (34985) (2 45 76 89 90)
      __divw clock timer (8273) (4 6 67 4 2)

but it is like this

      TMEmulation log_pseduo_allocation (34985) (2__divw 45clock 76timer (89 8273) 904) (6 67 4 2)

Any idea about the possible problem?

Thanks a lot in advance,
Patricia

Answer 1

A few possibilities all to do with the called program

1) as @Artefacto says the C++ program output might not be fully buffered so call setvbuf to make it consistant. ie the first output is partially buffered and second is not and so first flushes after the end of the second. In general buffering can differ if called from the command line and from a process.

2) The program is multi-threaded and the output behaves differently when called from java and so the output timing differs.

Basically you need to look at the code for the called program to force logging/output to be all through the same call.